The present invention relates to a heat treatment method for heat treating and depositing a thin film used for a gate electrode and wiring of a semi-conductor device.
In a semi-conductor device such as an LSI, a polycide layer having a polysilicon layer and a tungsten silicide layer given low resistance by doping impurities such as, for example, phosphorous, is widely used as a material for a gate electrode and wiring in order to lower resistance of the gate electrode and the wiring. The tungsten silicide layer as an upper layer of polycide structure is generally deposited by a CVD method using WF6/SiCl2H2/Ar as reactive gas. Thus when the tungsten silicide layer is deposited on the polysilicon layer, a deposition temperature, a reactive gas pressure, a gas flow rate, a gas flow rate ratio and so on are controlled to obtain required thin film properties of the tungsten silicide layer.
Since recent rapid development of microprocessing technology results in a requirement for further reducing the resistance of the gate electrode and the wiring, it has been tried so far to reduce the resistance of the tungsten silicide thin film by applying various conditions of the reactive gas (WF6/SiCl2H2/Ar). However if only an adjustment of compositions of the thin film by changing the conditions of the reactive gas is performed, the reduction of the resistance of the thin film encounters a limitation. Therefore it is difficult to reduce the resistance by the conventional method corresponding to the microprocessing and thin film thickness reduction that will further progress.
The present invention is to solve the above-mentioned problems and has an object to provide a heat treatment method for heat treating and depositing a thin film that ensures to realize lowering of resistance of the thin film and enables to correspond to the lowering of the resistance that will further progress from now on.
This invention is the heat treatment method for heat treating a thin film including a metallic silicide layer containing an element of Group V of the Periodic table comprising a heating step to heat the thin film to a predetermined temperature, a keeping step to keep the thin film at the predetermined temperature and a cooling step to cool the thin film from the predetermined temperature, wherein the thin film is heated in an atmosphere of gas which is oxidizing gas or contains oxidizing gas at least in the heating step.
The present invention is the heat treatment method for heating the thin film, wherein the thin film is provided on a silicon substrate.
The present invention is the heat treatment method for heating the thin film, wherein the thin film further has a polysilicon layer provided on the silicon substrate side and containing an element of Group V of the Periodic table.
The present invention is the heat treatment method for heating the thin film, wherein the thin film is kept and cooled in an inert gas atmosphere in the temperature keeping step and the cooling step, respectively.
The present invention is the heat treatment method for heating the thin film, wherein the thin film has a metallic silicide layer containing phosphorous atoms.
The present invention is the heat treatment method, wherein the oxidizing gas is oxygen gas and the gas containing the oxidizing gas is mixed gas comprising oxygen gas and inert gas.
The present invention is the heat treatment method for heating the thin film, wherein the thin film is heated to a temperature of 950xc2x0 C. to 1100xc2x0 C. in the heating step.
The present invention is a deposition method for depositing a thin film having a metallic silicide layer containing an element of Group V of the Periodic table comprising a step to depositing a thin film having the metallic silicide layer containing an element of Group V of the Periodic table, the heating step to heat the thin film to the predetermined temperature, the temperature keeping step to keep the thin film at the predetermined temperature and the cooling step to cool the thin film from the predetermined temperature, wherein the thin film is heated in an atmosphere of gas which is oxidizing gas or contains oxidizing gas at least in the heating step.
The present invention is the deposition method for depositing the thin film, wherein the thin film is provided on the silicon substrate.
The present invention is the deposition method for depositing the thin film, wherein the thin film further has the polysilicon layer provided on the silicon substrate side and containing an element of Group V of the Periodic table.
The present invention is the deposition method for depositing the thin film, wherein the thin film is kept at the predetermined temperature and cooled in the inert gas atmosphere in the temperature keeping step and the cooling step, respectively.
The present invention is the deposition method for depositing the thin film, wherein the metallic silicide layer of the thin film includes phosphorous atoms.
The present invention is the deposition method for depositing the thin film, wherein the oxidizing gas is oxygen gas, and the gas including oxidizing gas is the mixed gas comprising oxygen gas and inert gas.
The present invention is the deposition method for depositing the thin film, wherein the thin film is heated to a temperature of 950xc2x0 C. to 1100xc2x0 C. in the heating step.
We studied a conventional heat treatment method in various ways in order to solve a problem that a film deposition step provides a limitation to the lowering the resistance of the film. As a result we reached a conclusion that inert gas such as nitrogen gas which is used for adjusting properties of the thin film in the conventional heat treatment method is the cause of providing the limitation to the lowering the resistance. In other words, since the heat treatment of the thin film is performed in the inert gas atmosphere, one of the causes is considered to be a phenomenon that impurities such as the phosphorous atoms contained in the thin film and contributing to the lowering the resistance thermally disperse in the thin film during the heat treatment and escape from the thin film, and an effect of reducing the resistance by adding the impurities that should have been essentially obtained during the film deposition is obstructed. Thus we obtained information that we can prevent the impurities such as the phosphorous atoms from escaping from the thin film by performing the heat treatment of the thin film in a specified gas atmosphere, and realize the further lowering of the resistance of the thin film.
The thin film to be subjected to the heat treatment in the present invention is one having the metallic silicide layer containing an element of Group V of the Periodic table. The resistance of the metallic silicide layer was reduced by adding the element of Group V of the Periodic table, and it has been so far deposited in a known method. The elements of Group V of the Periodic table including phosphorous, arsenic, antimony, and bismuth have been widely used so far as a dopant of the thin film. And the thin film in the present invention is that containing at least the metallic silicide layer. Therefore the thin film in the present invention may be one made from the metallic silicide layer only, or one made from the polysilicon layer overlaid by the metallic silicide layer. The metallic silicides include, for example, tungsten silicide, titanium silicide, cobalt silicide and molybdenum silicide.
The thin film to be subjected to the heat treatment in the present invention is one having a polysilicon layer and a metallic silicide layer containing the element of Group V of the Periodic table. The polysilicon layer and the metallic silicide layer of this thin film contain an element of Group V. Both of these layers can be continuously deposited by same deposition equipment, or the polysilicon layer and the metallic silicide layer can be individually deposited by different deposition equipment. In either deposition method, an addition of the element of Group V to the metallic silicide layer enables to appropriately control a grain size and orientation of crystal and to obtain the stable layer having low specific resistance (resistivity) and excellent migration resistance. For example the tungsten silicide layer is preferable as the metallic silicide layer, and the phosphorous atoms are preferable as an element of Group V to be added to the tungsten silicide layer. The deposition method of the tungsten silicide film containing the phosphorous atoms has been already proposed by the present Applicant in JP 10-262307.
The heat treatment of the present invention is performed in an oxidizing gas atmosphere or a gas atmosphere containing the oxidizing gas. The heat treatment step comprises the heating step to heat the thin film to the predetermined temperature (for example 950xc2x0 C. to 1100xc2x0 C.), the temperature keeping step to heat treat the thin film while keeping the heat treatment temperature after the heating and the subsequent cooling step, wherein the oxidizing gas or the gas containing the oxidizing gas is used at least in the heating step. The oxidizing gas comprises the oxygen gas, and the gas containing oxidizing gas comprises the inert gas such as nitrogen gas mixed with the oxidizing gas such as oxygen gas, and an oxide film is deposited on the thin film by the heat treatment of the thin film in the oxidizing gas atmosphere or the gas atmosphere containing the oxidizing gas. This oxide film can prevent the element of Group V such as phosphorous atoms from escaping from the thin film, and consequently realize the further lowering of the resistance. The heat treatment equipment used in the present invention is of a sheet-fed type (single type) using a halogen lamp or the like or of a batch type using a dispersion furnace such as an electric furnace. The single type of the heat treatment equipment is preferable considering a size enlargement of a semi-conductor wafer from now on.
The heat treatment method of the present invention uses the oxidizing gas or the gas containing the oxidizing gas at least in the heating step of the thin film. In the heating step, since the film is heated to the heat treatment temperature of, for example, around 1000xc2x0 C., the oxide film is deposited on the thin film by using the oxidizing gas or the gas containing the oxidizing gas in the heating step before starting the temperature keeping step. Therefore the inert gas such as the nitrogen gas not containing oxidizing gas may be used in a step after the heating, namely in the temperature keeping step to keep the heat treatment temperature of, for example, around 1000xc2x0 C. and the subsequent cooling step. Since a surface of the thin film is already protected by the oxide film in the heating step, escaping of the element of Group V such as phosphorous atoms can be prevented even if the inert gas such as the nitrogen gas is used in the step after the heating, and the further reduction of the resistance can be realized.
It is preferable to use the oxidizing gas or the gas containing the oxidizing gas only in the heating step and to use the inert gas such as the nitrogen gas in the step after the heating in the heat treatment method of the present invention. That is to say, it is preferable to use the inert gas such as nitrogen gas in the temperature keeping step and the cooling step after the heating. Particularly, in the sheet-fed type of the heat treatment, since the heat treatment is performed for a short time by RTA (Rapid Thermal Annealing), distribution of the specific resistance in a semi-conductor wafer becomes uneven, and variation of the specific resistance tends to become large. However, usage of the inert gas in the step after the heating can alleviate a disadvantage of RTA and drastically restrict the variation of the specific resistance of the entire surface of the semi-conductor wafer.